The invention relates to a method for applying a coating to an object in which a particulate coating-material is conveyed along a transfer conduit by means of a fluid flow and is discharged from the line in a coating zone. The invention also relates to an apparatus for applying a coating to an object in which a particulate coating-material from a feed bin is conveyed along a transfer conduit by means of a fluid flow from a fluid source and, in a coating zone, is discharged from the line and impinges on the object to be coated.
Methods and apparatus of the said kind for the coating of objects are known. The coating particles are applied to the object to be coated, often under the influence of electrostatic charge, and yield a durable coating, eg. after heat treatment. In particular, such a process is known for the coating or spraying of the internal seams of can bodies, or of the entire internal wall of can bodies, with coating material. In the process, the coating material, usually a powder, has to be conveyed along an extended conduit, as the only way to gain access to the closed body of the can is through the welding machine. This long conduit requires the fluid, usually air, to be conveyed at high velocity in order to carry the powder in sufficient quantities along the extended conduit. However, a high air velocity or particle velocity at the discharge point is disadvantageous, since it may cause the powder particles to bounce off the surface to be coated, thus reducing the efficiency of the coating process. Furthermore there is a requirement that the coating material should be distributed as uniformly as possible at the point of discharge and upon impact on the object to be coated, in order that a coating of uniform thickness can be obtained; this is especially necessary when coating seams of can tubes or bodies.
It is therefore the object of the present invention to provide a method and an apparatus whereby high coating efficiency can be combined with good conveying conditions in the conduit, and whereby a highly uniform coating can be obtained.